1. Field of the Invention
The invention relates to a speaker apparatus.
2. Related Art
A speaker apparatus utilizing cone paper as a diaphragm is called as “cone-type speaker apparatus”. FIG. 1 is a partially cross-sectional diagram for illustrating a general configuration of a conventional cone-type speaker.
A speaker apparatus 51 comprises a frame 53 and cone paper 52 that is concavely installed to the frame 53. It also comprises a bobbin 55, which is positioned behind the cone paper 52, and a voice coil 54 wound to the bobbin 55. The bobbin 55 is suspended on the frame 53 by a damper 56.
It further comprises a yoke 57, a magnet 58, and a plate 59, which are composed of magnetic circuit and set behind the frame 53. They convert an electric signal applied to the voice coil 54 to a linear movement of the bobbin 55 so that the cone paper 52 can vibrate to sound.
The cone-type speaker apparatus may make the magnetic circuit smaller if the cone paper could vibrate by small magnetic flux. Therefore, the cone paper is made to be very thin so that it is as lightweight as possible. The cone paper is then shaped into cone to strengthen.
In the cone-type speaker apparatus, if a scale of the magnetic circuit is constant, in order to make the entire speaker apparatus thinner, the cone paper 52 may be made curved gently. Strength of the cone paper 5, however, deteriorates into a condition that a surface of the cone paper cannot uniformly vibrate, thereby generating distortion to make its sound quality deteriorated. Alternatively, if thick cone paper is used in order to strengthen it, the cone paper is made heavy weight, thereby causing its sound pressure to be decreased.
The damper 56 is used for suspending the bobbin 55 to which the voice coil 54 is attached. The damper 56 has an effect on reproduction capacity within a low frequency range in the speaker apparatus 51. In order to improve the reproduction capacity of the low frequency range, it is necessary to decrease its lowest resonant frequency, f0.
The lowest resonant frequency, f0 is represented as follows:f0(Hz)=½π√s0/m0
where m0 (g) is effective mass in a vibration system such as the cone paper 52 and s0 (dyne/cm) is stiffness of vibration-member-suspending part(s) such as the damper 56.
If the effective mass m0 is constant, it is necessary to decrease the stiffness of the vibration-member-suspending part(s). The damper 56 and edge portion 52a are illustrated as the vibration-member-suspending parts. In general, the stiffness of the edge portion 52a is less than that of the damper 56, so that decreasing the stiffness of the damper 56 allows the reproduction capacity in the low frequency range to be improved.
When the entire conventional speaker apparatus 51 is made low-profiled, a distance between an adhered point A of the bobbin 55 and the cone paper 52 to which an end of the damper 56 is attached, and an attached surface B of the frame 53 to which the other end of the damper 56 is attached is not sufficiently gained.
In order to decrease the stiffness of the damper 56 to improve the reproduction capacity in the low frequency range, it is conceivable to make the damper 56 thinner. If making the damper 56 thinner, however, its strength deteriorates.
If the bobbin 55 is made higher, the damper 56 may be made longer, thereby decreasing the stiffness of the damper 56 so that f0 decreases. This prevents the entire speaker apparatus from becoming a low-profile one.
FIGS. 2A and 2B are partially cross-sectional diagrams each for illustrating a general configuration of a conventional cone-type speaker apparatus having a magnetic-proof system.
Conventionally, in order to have the cone-type speaker apparatus 51 provided with the magnetic-proof system, a cancel magnet 60 is set behind the yoke 57, as shown in FIG. 2A. Alternatively, a cover 61 is set to make a magnetic shield on the entire magnetic circuit, as shown in FIG. 2B.
Using the cancel magnet as shown in FIG. 2A causes the entire speaker apparatus to be made thicker. Using the cover 61 as shown in FIG. 2B causes a magnetic path to be formed, as shown by arrows therein, so that the magnetic flux is dispersed and sound pressure of the speaker is reduced.
In order to improve the above problems, it has been proposed that speaker apparatus, which is called as “reverse cone-type speaker apparatus”, having the cone paper installed convexly is provided.
The reverse cone-type speaker apparatus can hold the frame portion low-profiled so that a low-profiled speaker can be implemented. It, however, makes the bobbin higher, thereby resulting in the cause in the bobbin's lateral vibration. This causes the voice coil to be contacted with the plate, thereby becoming worse in sound quality.
If the bobbin is made lower, it may prevent the bobbin from laterally vibrating. Since, however, the damper cannot be made longer, this avoids the reproduction capacity in the low frequency range and properties for input power handling being improved.
It is an object of the present invention to present a speaker apparatus having the cone paper installed convexly whereby even if the bobbin is made higher, it prevents the bobbin from vibrating laterally.